Process of liberating fiber from bagasse or like stalks



Patented June 30, 1931 UNITED STATES PATENT OFFICE GEORGE A. RICHTER, 0F BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE PROCESS OF LIBERATING FIBER FROM BAGASSE 0B. LIKE STALKS 110' Drawing.

This invention relates to the liberation oi fiber from bagasse or like fibrous stalks, and has for its object the production of fiber suitable for the manufacture of salable papers by effective and practical procedures.

Heretofore, in producing fiber from batures and pressures that the OH ions in the the alkaline liquors not only efiect a solution of the encrusting material, but also produce sufficient hydrolysis of the cellulose to shorten the fibers appreciably. The so-called acid sulphite process of fiber liberation is still more unsatisfactory, probably because the H ions in such liquor produce an even greater hydrolysis of the cellulose and because the silicious content of the bast fibers interferes with the penetration of acid cooking liquors more than of alkaline liquors which are capable of dissolving such content. Furthermore, the fibers of bagasse or like stalks are initially considerably shorter than wood fibers such as spruce, and in order to produce a commercially valuable fiber it is necessary to preserve the initial length of fiber as much as possible.

I have found that if bagasse or like stalks are digested in alkaline solutionsof an alkalinity considerably greater than the alkalinity of the usual soda or kraft liquors, but at temperatures considerably lower than those maintained during soda or kraft digestion, a liberation of fiber maybe effected to produce a high yield of fiber of a length materially greater than fiber produced from such sources by the usual alkaline processes. Thus, by digesting bagasse in liquors of sufficient alkalinity, a fiber liberation may be effected at atmospheric boiling temperature in a relatively short period of time, to produce fiber of a quality suitable for manufacture into wrapping and bag papers. Liquors of the alkalinity of the usual Application filed January 20, 1927. Serial No. 162,417.

soda or'kraft liquor will not effect fiber liberation under such conditions.

Bagasse, which is available in large quantities as a cheap waste material from sugar refineries, ma 1 be treated with or without previous contitioning by my process, For instance, the bagasse may or may not be dried and freed from residual sugar and pith; but to produce a finished product of optimum strength, the pith is preferably removed, as by drying the bagasse and then dusting, or separating the pith, as by blowing it from the bagasse by a current ofair or other gases.

The applicability of the process of the present invention may best be appreciated by, reference to a specific example of procedure which has been found to give proper results in practice, such as the following. The bagasse, previously conditioned if desired, is charged into a liquor initially containing from 7% to 12% caustic soda equivalent in the form of either caustic soda or sodium sulphide, alone, or in admixture. Such a liquor is far more concentrated than the liquor employed in the soda process, which usually contains from 3% to 4% caustic soda equivalent, or that employed in the kraft process, which usually'contains about 5% caustic-soda equivalent in the form of caustic soda and sodium sulphide. Whereas soda or kraft cooks are carried out at temperatures of about 335 F., at pressures of about 100 pounds, for from three to five hours, the cook, in accordance with the present invention, is effected at temperatures not above atmospheric-boiling point, and, in fact, at temperatures down to as low as 70 C., for I have foundthat a complete fiberliberation may be effected under such conditions, using a liquor-of high alkalinity, in a period of from four to eight hours.

In cooking, the charge may be raised to the maximum temperature of cook desired in one or more steps. For instance, rather than raising the charge directly to atmospheric upon the charge may be raised to the desired cooking temperature and maintained thereat for from four to eight hours. This latter procedure results in a higher yield of a better quality fiber than when a cooking temperature of, say, 100 C. is reached by direct step, and the complete cook is effected in a period of time of from six to eight hours. If a twostep procedure is practiced, the steeping treatment at room temperature is preferably carried out in a more concentrated liquor than that in which the subsequent cook at elevated temperature is effected, as a more concentrated liquor promotes a more r apiddiffusion or penetration of the liquorinto the stalks. The concentrated liquor may be diluted after the initial steeping treatment to the desired cooking concentration.

A process such as herein described is eminently more suitable than the usual kraft 0r soda processes for efi'ecting a fiber liberation from bagasse or like fibrous stalks, as by such latter processes there is a pronouncedly greater degradation of cellulose fiber, which is initially of short length; that is to say, a far more drastic action on the cellulose fiber of a high-pentosan-containing material, such as bagasse, is etlected at high temperature with weak alkaline solutions at elevated temperatures and pressures than with more concentrated alkaline solutions at lower temperatures and at atmospheric pressure. Thus, by my process, I obtain a higher yield and a much stronger fiber from bagasse than when the usual kraft or soda processes are employed in the production of such fiber. In actual practice, I have obtained 45% to 60% yields of a fiber which is suitable for the manufacture of salable wrapping and bag papers, which, when tested in the usual way, show strength and tear values equal to those obtained from an unbleached sulphite pulp paper. The fiber has a total cellulose content of from" 85% to 95% and a pent-osan content of from 8% to 11%, these latter values exceeding the pentosan content of the usual kraft pulp. By closely regulating the cooking conditions at atmospheric pressure, the characteristics of the fiber may be controlled. For instance, if it is desired to produce a fiber for use in the manufacture of wrapping papers where color is unimportant, the temperature of cook and concentration of liquor are maintained at lower values, which act to produce strong, tough fiber in a reasonable period of time.

The resulting fiber is separated out from the spent digesting liquor, which latter may be subjected to the usual regenerating or recovery processes employed in a soda or krat't mill for the recovery of its valuable constitucuts. The separated fiber is washed. but may or may not be screened, as it maybe desirable to retain the long, wirv and tough bust fibers tolendreinforcem ntthereto. lVhenthcbast fibers are retained, they may be somewhat disintegrated by subjecting the fiber to a disintegrating device, such as a kollergang, prior to formation into paper.

Although a fiber liberated from high-pentosan-containing cellulosic material such as bagasse is unbleachable without permanentl ,"impairing its paper-making characteristics, nevertheless it is possible to lighten the color of the liberated fiber by adding a suitable amount of an oxidant, such as sodium hypochlorite, to the cooking or fiber-liberating liquor. This may be done only when caustic soda or like chemical is alone present in the liquor, as sodium sulphide, sodium sulp'hite, or like reducing salt reacts with the oxidizing agent and produces an inactive salt. It a two-step procedure is practised, it may be desirable to add the oxidant to the liquor while the charge is maintained at about room temperature, as a more selective or pre terential reaction upon ligneous or coloring material ensues at such temperature; but if the bagasse is highly colored or refractory, it may be necessary, in order to produce fiber of the desired whiteness, to add the oxidant to the liquor while at elevated temperature. The amount of sodium hypoehlorite added may vary from 5% to 10%, depending on the whiteness of fiber which it is desired to produce. Other oxidants, such as sodium peroxide and sodima'permanganate, may be substituted in lieu of part or all of the sodium hypochlorite.

The procedure hereinbefore described for producing a light-colored fiber may be modified, if a two-step procedure is employed. For instance, the bagasse may be steeped first in a concentrated liquor at about room temperature, as described. The semi-treatmi stalks are then separated from the liquor, washed, and disintegrated or defibered. if desired, as by means of kollergangs. The stalks or fiber are then treated with halogenizing or oxidizing lignin-reactive reagents, 0. g., chlorine water, or hypochlorite solution, washed and cooked at elevated temperature in an alkaline liquor, which may be the initial concentrated liquor diluted to contain about 7% to 12ft caustic soda equivalent. If desired, oxidant may also be present in the alkaline liquor during the initial and final treatments, or both, but it may be distinctly advantageous to follow the procedure wherein the halogenizing or oxidizing treatment of the stalks or fiber is effected between successive alkaline treat ments, as such 'irocedure does not entail the introduction of chlorine-containing com pounds: in the cooking liquor, so that the usual processes may be employed in recovering the valuable constituents of the spent liquor.

One of the important adiantages ot the. process hereinbefore outlined, is that if practised at atmospheric pressure, it may be carried out continuously and economically in open tanks, or in apparatus such as disclosed in my application, Serial No. 128,- 398, filed August 10, 1926.

lVhile I have described my process as being especially advantageous in effecting a fiber liberation from bagasse, it should be re marked that it is also applicable in connection with bamboo, corn stalks, straw, or similar monocotyledons. i v

Having thus described the process of my invention, it should be understood that it is capable of change and modification without departing from the spirit or scope of invention as defined by the appended claims.

I claim:

1. A process which comprises steeping bagasse or similar monocotyledons at about room temperature in an alkaline liqour of an alkalinity we at least 7 caustic soda equivalent until such liquor has difi'used into and penetrated such stalks, and'then cooking such stalks at atmospheric pressure in such liquor.

2. A process which comprises steeping bagasse or similar monocotyledons at about room temperature in a highly concentrated alkaline liquor until such liquor has diffused into and penetrated such stalks, then diluting such liquor to an alkalinity of about 7% to 12% caustic soda equivalent, and cooking such stalks in such diluted liquor at atmospheric pressure.

3. A process Which comprises steeping bagasse or similar monocotyledons at about room temperature in a liquor containing an oxidant, separating out and treating the stalks with a lignin-reactive reagent, and then cooking such stalks at atmospheric pressure in an alkaline liquor.

4. A process which comprises steeping bagasse or similar monocotyledons at about room temperature in a liquor containing an oxidant, separating out and treating such stalks with a lignin-reactive reagent, and then cooking such stalks at atmospheric pressdure in an alkaline liquor containing an oxiant.

5. A process which comprises steeping bagasse or similar monocotyledons at about room temperature in an alkaline liquor containing an oxidant, and then cooking the stalks at atmospheric pressure in a liquor containing 7% to 12% caustic soda equivalent.

6. A process which comprises steeping bagasse'or similar monocotyledons at about room temperature in a concentrated alkaline liquor, separating out and treating the stalks with a lignin-reactive reagent, and cooking such treated stalks at atmospheric pressure in said first-mentioned liquor.

7. A process which comprises steeping bagasse or similar monocotyledons at about room temperature in a highly concentrated I GEORGE A. RICHTER. 

